Moirai

An Extensible Pure Operation-Based CRDT Framework for Building Collaborative Applications

Features • Quick Start • Architecture • Documentation • Publications

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⚠️ Work in Progress — In Development ⚠️

This project is under active development. This project is currently under active development. The API and features are subject to change as we refine the framework.

Overview

Moirai is a Rust-based framework for building pure operation-based Conflict-free Replicated Data Types (CRDTs). It provides a flexible, extensible architecture that enables developers to create custom CRDTs with sophisticated conflict resolution semantics, making it ideal for distributed collaborative applications.

Features

Core CRDTs

Moirai provides a comprehensive library of CRDT implementations:

Category	Types	Description
Counters	Counter, ResettableCounter	Increment/decrement with optional reset
Flags	EWFlag, DWFlag	Enable/disable boolean flags.
Registers	MVRegister, TORegister, PORegister, Last-Writer-Wins Register, Fair Register	Multi-value, semantically data-driven totally ordered and partially ordered registers, unfair and fair to process single value registers.
Collections	AWSet, RWSet	Add-wins and remove-wins sets
Maps	UWMap	Update-wins map with nested CRDT values
Graphs	UWMultiDigraph	Directed multi-graphs with CRDT nodes and edges
Lists	List (EG-walker), NestedList	Collaborative text editing with nested structures
Composite	Union, Record	Sum types and product types CRDTs
Document	JSON	CRDT for JSON-like hierarchical documents with rich data types

Most of these CRDTs implementations are based on specifications that have been formally verified using VeriFX.

Quick Start

Installation

Add Moirai to your Cargo.toml:

[dependencies]
moirai = { git = "https://github.com/CEA-LIST/Moirai.git" }

Basic Example: Counter CRDT

use moirai::{
    crdt::counter::simple_counter::Counter,
    protocol::{
        crdt::query::Read,
        replica::IsReplica,
        state::po_log::VecLog,
        broadcast::tcsb::Tcsb,
    },
};

// Create two replicas
let (mut replica_a, mut replica_b) =
    moirai::crdt::test_util::twins::<VecLog<Counter<i32>>, Tcsb<Counter<i32>>>();

// Replica A increments
let event = replica_a.send(Counter::Inc(5)).unwrap();
replica_b.receive(event);

// Replica B increments
let event = replica_b.send(Counter::Inc(3)).unwrap();
replica_a.receive(event);

// Both replicas converge to the same value
assert_eq!(replica_a.query(Read::new()), 8);
assert_eq!(replica_b.query(Read::new()), 8);

Architecture

Moirai's architecture separates concerns into distinct layers:

┌─────────────────────────────────────────────────┐
│            Application Layer                    │
│  (Your collaborative application logic)         │
└─────────────────────────────────────────────────┘
                      ▼
┌─────────────────────────────────────────────────┐
│         CRDT Layer (IsLog + PureCRDT)           │
│  Counter │ Map │ Set │ List │ Graph │ ...       │
└─────────────────────────────────────────────────┘
                      ▼
┌─────────────────────────────────────────────────┐
│       State Management (EventGraph/POLog)       │
│  Causal tracking │ Operation storage            │
└─────────────────────────────────────────────────┘
                      ▼
┌─────────────────────────────────────────────────┐
│     Protocol Layer (Replica + Broadcast)        │
│  Version vectors │ Causal delivery              │
└─────────────────────────────────────────────────┘

Publications

Moirai has been used in the following research:

• Léo Olivier, Kirollos Morcos, Marcos Didonet del Fabro, Sebastien Gerard.
  A Local-First Collaborative Modeling Approach with Replicated Data Types.
  CoPaMo'25 - International Workshop on Collaborative and Participatory Modeling, October 2025, Grand Rapids, United States.

License

This project is licensed under the Apache License 2.0. See LICENSE for details.

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Acknowledgments

Developed at CEA LIST, the French Alternative Energies and Atomic Energy Commission.

Authors:

• Léo Olivier (@leo-olivier)
• Kirollos Morcos (@KirollosMorcos)

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